Radio frequency deflecting cavities are widely used in particle accelerators for beam manipulations. Superconducting structures extend the application areas of such devices to high duty factor and large beam current regimes, providing efficient and high gradient operations simultaneously. However, superconductivity adds complexity to the design of radio frequency (RF) cavities because of limitations associated with the maximum allowable surface magnetic field.
Alternative solutions based on the transverse TE11 magnetic mode and TEM lines have been proposed for the deflection of charged particles. Such approaches may result in smaller cavity design compared to the conventional TM11 elliptical cavity and eliminate the presence of LOM modes. However, these new designs are still comprised of a closed resonant volume with a dense eigenfrequency spectrum, and therefore require auxiliary couplers for damping coherent high order mode excitation.
Pill-box type resonators with an elliptical shape, operating in the dipole electric TM11 mode, have been used for beam deflection. Despite its simple geometry and good surface cleaning capability, there are a few major drawbacks to such designs. First, the TM11 mode is not the lowest mode in the cavity spectrum. Additionally, a number of Low Order Modes (LOM) and High Order Mode (HOM) couplers are required for damping unwanted resonances. Further, such cavities have large transverse dimensions. Thus, there are difficulties with the cryostat design, which complicates cavity operation. Thus, there is a need for a simple and compact superconducting structure for beam manipulation applications.